Supervisory system.



M. S. CUNNER.

SUPERVISORY SYSTEM,

APBLIOATION FILED MAE. 5. 1904.

Patented 0013. 20, 1908.

. w W w & m y m wwmw EMM W UNITED STATES PATENT OFFICE.

.MERRITT s: connnn, QFYCHICAGO, ILLINOIS, ASSIGNOR T 'S'lROMBERG-CARLSON TELE- PHONE MANUFAGTURING'COMIfANY, 0F nocnnsrnn-wnw YORK, A CORPORATION or N EW YORK To all whom it-may Be it known that I,"MERRI'1T S. GoNNnR, citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented acertain new and useful Improvement in Supervisory Systems, of

which the following is a full, clear; concise, and exact description, reference being had to the accompanying drawings, forming a, part of this specification.

' My invention relates to telephone er-' change systems, and particularly to an improved supervisory signal for use in conj unc *tion therewith V In accordance with my invention any de-.

sired supervisory signal may be employed,

such, for instance, as a small incandescent -by' reference to the acompanylng drawing, which diagrannnatically re resents a central energy exchange system with two subscribeis. lines terminating therein and in which I have shown at each of the substatlons A and B a well known form of substation apparatus for use with central energy systems.

Each of the substations is provided with a switch hook 1,.which, when in its normal depressed posit-ion connects a condenser 2 and call bell- 3 between the: line-limbs 'and 5 leading to the central station. When the receiver (i is removed from the switch-hook 1' circuit for continuous current is closed between the line limbs and through thetransmitter' 7 and primary 8 of the induction coil,

whose secondar 9 -is connected with the receiver (3. The ine limbs 4 and 5 terminate respectively at the central station in back contacts 10 and'll of a 'cut-ofi relayywhos'e iti've' line limb 4, while the line limb .5 is connected with the associated sleeve springs 19, 19,.

The test thimbles 2 0, of these Specification of Letters Patent. A uma nmm mi; 5,1904. a 198,726. b

etic switching de- 3 3 are connected togetherand thence snrnnvr'somr szsrnm. y

.- Patented 005.20,; 1908.

V thehvindingfli o fjthecutbfi relay 22 with the positive pole of;.the battery. The line relay-l6 controls by means of its armature 23 and contact alocaL circuit through the 1ine signal ing. lamp 25-].The line circuit/60 which I have thus described is well adapted for use with my invention, as are the majority of common battery line circnitswhich 'haveheretoforeibeen pro'posed. The opera tors cord circuit compr ses anv answering 6'5 plug 26 and ajcallingplug 27, the tip .contacts .28an'd; 29 of which are connected by means of-a tip strand comprising the sections 30 and 31, thesesections being cd'nductively interrupted-by tlie.s"eria1.;inc1usi on of a c0n-. 7o

denser 32.- l f V i v The sleeve contacts 33 and 34 are connecte'df-by means of the; sections 35' and 36 of a sleevestrand between which a condenser 37 is connected. The'-'usual ringing and listening key .is provided,,the. spreadmg of the springs serving to connec t -thegenerator 39 in bridge of the strands leading to the 'calling plug. Thelsprea'ding of the springs 39 serves to' connect the operators telephone set 40 in bridge of" the strands. An additional spring ilis provided for. the listening key, this spring operating in conjunction wit-ha contact .42. The spring 41 normally makes contact. with the spring 39 connected with-tlietip strand, and is adapted to remain in contacttherewith until it engages spring42 when the key is actuated. The contact 42-is connected through a test windingracf the induction coil of the op-' era'tors" set with the positive pole" of the battery by means of a conductor 44;

My present invention provides a positivedouble supervisory system .in accordance with" whichtwo" supervisory lamp signals. are provided,f,one controlled from each side of the circuit. The supervisory la'mp- 4:5

is connected in 'alocal circuitwith the batvt'ery-andthe contact'springs' 46 and 47. In

the sameway the eryi'sory lamp 48',i's included in a circuit with the contact springs ism-1a 50. The closure'of the springs closes thecircuit tlnoughf the associated supervisory lampi causing the sameto be illumimated to give a; Each of the snpervisoiy-lamps is controlled" by a compound relay, which. may, be described as follows:

The relay 51 is connected between the ale of, the "battery and the sec fi we hae. en me M1 r.

.- no respectivel quit. The relaywi-nding 52 connected be tween the positive pole-of the battery -and the sect1on 30'of-,.the; tip'strand, of the cord The armature is provided with the. i5 armature tongues 53 and 54.'-'-I;The stud 55 is .7 58 being connec by means'ofthe con.

jductor 59=with the contact -spring ii of the listening key. The s ri 56' of the relay associated with the plug is connectedv by means of the conductor 60 with the-tip as strand of the cord-circuit, whic is to the right "of the condenser32. e

The operation of this system'to which in invention may at substation A, desiring connec- 153) tion, removes his-receiver from the switch hook, thereu 11' closing the line circuit through the lme rela tion with'its front contact 24, thus closing the localicircuit through the line lamp and. causing the illumination thereof. The operator responds to-this signal by insertthe answering plug 26 in the answeringcl rof the lineto' substationA, whereupon so the 'followigg circuit is-clos'ea'dzirom the neg- ..ative pole the batterythrou h. the win 51* of the compound relay, t ence,to. section of the sleeve'strand, through sleeve contact 33,'thimble 20 and winding 21 of the at u -0 relay t6 h p s r of the et:

' Thepassage' of currentthrough this .clrcuit causes the ener ization ,of the cut-ofl relay 22, whereupon the armatures 12 and linre withdrawn from their back contacts thereby interrupting the .continuity o the otherwise closed circuit through the line-relay and permitting a deenergization thereof. The energizatlon of the cut-off relay atthe same time breaks the direct connection between the line limbs and the battery. The energization ofthe relay due to the passage of current through its;

iwinding 51 causes a downward attraction of the armaturetbngue. 54, the movement bit the tongue being As the studj55 is'withdraWn from the under side of the vtongue 53, thistongue 53 would naturally drop,with the tongue -54, thereby permitting the contact spr ng 46 to 6511 t into-connection the contact be applied is as follows: f

16. The armature of the line relay is there y'brought into connec--- opposed by the spring vention of the, column 61; This closure of the circuit through the contacts 46 and 47 1, line limb 5, sleeve, spring 19, and thence through thesleevestrand. 35. and winding 51 to the negative pole of the battery. The current .flowing through .this winding 52 causes an upward attraction of the tongue 53,whei'e'upon the circuit through the springs 46 audit is prevented from closing. It will be noted that thecircuit through the winding ,5l-is controlled by the operator by means "of the connection between the sleeve contact of the plug and the thimble of the line jack, whereas the circuit through the winding 52 is controlled by means of the switch at'the. substation. In establishing a connection, therefore, with a calling line, no illumination of the supervisory lamp 45 will be caused.- The operator, after inserting her plug, manipulatesher listening key to connect her telephone set in bridge ofthe cord strand and thereuponlearns the number of the line with which connection is desired.

Upon learning that theline of substation B is desired, the-operator first applies the tip' contact of the' calling plug to a test thimble 20 of one of the multiple line jacks associated with the line of substation B. In doing so the listening key is left in the open ositlonconnecting the operators set in ridge of the cord strands. If the telephone line is not busy, the potential of the test thimbles will be that of the positive grounded pole of the battery by reason of the connection therewith. As the test winding-43 is-also connected through the conductor 44 with the same pole of the battery, there will be no click in theo'perators tele= -phone receiver. She thereupon inserts the calling plug in the multiple jack and mavnipulates her. ringing 'key to call the subscriber. o Upon inserting the calling plug 27 in a multiple jack, the following circuit is closed: from the negative pole. ofthe common bat- "through the winding 2l of'the cut-01f relay 22 ofline of substation B, to the positive pole of the "battery 13. The current flowing through this circuitienergizes the cut-off re-.

.47, the movementof the spring 46 being con -t1;olled bv the tongue through the inter-- tery through the winding 51 of the com- 40 of the cut-.0

emu/in cor-r lay, whereupon its aruiatures are attracted, and also causes the desired attraction of the armature tonguefzl' of'the compound re- The withdrawal ofthe stud 55' from the under side of the-armature; tongue 5 3' permits this latter ton ue .-'to drop, thereby" 9 conductor '60 to the section 3l'jof, the tip strand, tip contact 29, tip spring- 17 [of the naultiple jack, line limb '4, transmitter. 7, primary" winding, 8 and switch hook I at su-bstation'Bgline limb 5, sleeve spring 19- of the multiple jack, sleeve contact 34, section' 36 f the sleeve strand, conductor. 62, and winding sl'ito the negative pole of the battery. Current flowing. through this circuit energizes the co'mpound relay -insuch a .way' as tocau'se the upward movement of the ttmgue 53"; whereupon the circuit established through the supervisory'lamp 48 and the contacts-'49 and O- isbroken, the supervisory lamp be .extinguzisheithereby. The removal'of't e reeerver'from the switch hook at substation B does not causetlie 1llumina-' tion of its line lamp signal 25,-.for the reason thatthe circuit through the line relay 16 haspreviously -o ned due to the energization 1 f relay 22'. Eitherlsubscriber, upon replacing his telephone upon the switch hook, iopens the circuit .throu h the compoundfirelay winding controll by the. sub- 'scribers switch, whereupon theupper arma ture tongue is permitted to dropupon the insulating stud 55 or 55, as the case'may be, -whereupon the associated local superv sory circuit is closed through the supervisory lamp to indicate to the operator that the sub- 50 scriber has finished this conversation. The

' removal of the cord plugs from. the jacks causes thed nergiza-tion of the associated relay wind' tion, whereupon the lower armature ton ue 65 is forced into its normal positioniby he,

spring 56 or 56', as t-he'case may be, whereupout-he local supervlsory c1rcu1t 1s agam opened and the supervisory .lamp .extin 'guished. 60 The drawing lllustratmg my invent on shows its use in conjunction with a certain feature/of the busy test circuit, which I shall now describe. In the first place, it will be noted that the insertion of a plug within a line ack causes a change inthe potential of controlled from the substa senses 8 the thimbles of these jacks, dueto the circuit whichis established throughthe cut-off relay winding, thesleeve strand of the cord circuit, and oneof the windings of the compound relay; Normally-the potential of the test thimbles is that of the positive grounds ed pole ofthe battery, but upon'the closure of thiscircuit the potential is changed and ,thischange of potential is used in making the busytest. The operator, after manipu- Iating'herliStening key to ascertain the number of'the line wanted, applies the tip con tact 29 of the calling plug to the multiple jack thimble. s p V If 'a connecting plug at some other 'posi- .tion of the multiple switchboard has already been'inserted in one of the associated multiple jacks, a circuit may be traced ,as follows from the negative pole of the battery throu b one winding of the compound relay oi the other cord circuit, to the sleeve contact of the other, plug, and theme from the testthimble of the pack already in use 'to the test thimble with whose jack it is desired to make connection, thence to the tip contact 29 of the calling plug, through the tip strand 31, contact spring 41, and, due to thefopen condition of thelistening key, to contact -12, and thence through the test winding43- and conductor 44 to the positive pole of the battery. The passage of current through this circuit will cause a click in the operators telephone to notify her of the busy condition of the line. It will be noted that the manipulation of the listening key in making this busy test closes the test circuit and opens circuit through the tip strand of the cord circuit, this circuit being open on account of the break between the contact spring 41 and the upper spring 63 of the listening key. It is desirable that afterthe insertion of the calling. plug within the jack of aline which is not busythe operator be provided with means by which she may listen in upon the line. In order therefore to 10 maintain the continuity of the tip strand of. the cord. circuit after the insertion of a calling plug, the cont-act 58 is provided upon the compound relay associated with the calling plug. Upon the .insertion of this plug the consequent 'energization of the compound relay due to current passing through the winding 51 causes a downward movement of the spring 56', whereby the following circuit is established: .from theright hand side of I20 the condenser 32, through conductor 60, spring '56, to the contact 58 and conductor 59, tothe section 31' of the tip strand of the cord circuit. The closure of this-circuit prevents the break which would otherwise be introduced upon the manipulation ofthe listening key, thereby enabling the operator to listen in without interfering with the continuity of the talking circuit connection;

While I have herein shown and described 131 a preferred embodiment of my invention, it

will be readily understood that its application to other telephone circuits and systems is quite within the skill of those familiar with the art. I do not, therefore, wish to limit myself to the precise disclosure herein set forth, but

Having described my invention, I claim as new and desire to secure by Letters Patent:-

1. In a telephone exchange system, thecombination with a telephone line extending from a substation to a central station, of cord connectingapparatus at the central station for connecting said line with another, a: supervisory signal, an armature absolutely controlling a. circuit through said signal, an electromagnet for controlling said armature, a second armature controlled by a second elcctroma net, a mechanical connection between said armatures whereby said first ar-' -1nature is mechanically controlled by said second armature, an electric circuit including part of the talking circuit closed through said second electromagnetvupon the connection of said cord connecting apparatus with said line, and an electric circuit through said first electromagnet controlled by a switch at the substation.

2. In a telephone exchange system, the combination with a telephone line extending from a substation to a central exchange, of cord connecting apparatus at the central exchange for connecting said linewith another, a supervisory signal, an armature absolutely controlling the circuit through said supervisory signal, an electromagnet for said armature, a second armature having normally mechanical engagement with said first armature, an electromagnet for said second armature, a circuit including part of the talking circuit closed throu'gh said second electromagnet upon connection of said cord connecting apparatus with the line, whereby said second armature is act-uated and the mechanical connection between the armatures removed, and a circuit through said first .electroina-gnet closed upon actuation of substation apparatus.

In a telephone exchange system, the

combination with a telephone line extending from a substation to a central exchange, of cord connecting apparatus at the central exchange for connectingsaid line with another, a supervisory signal, a unitary electromag netic device for controlling the 'circuit through said signal, two electromagnet coils for said device, an armature associated with one coil, switching mechanism included in the supervisory signal circuit and absolutely controlled by said armature, an armature for the second coil having normally mechani al connection with said first armature, switching mechanism for said second coil adapted through said mechanical connection to, normally cause the supervisory circuit to be opened at the switching mechanism of the uding part of the- .talking circuit. closed throughsaid second coil upon connection of the cord connecting first coil, a circuit inc apparatus with the line whereby the corresponding armature is withdrawn from said mechanical connection with the first armature and the supervisory circuit al'- lowed to. be closed, and a circuit closed through said first coil upon actuation of substation apparatus, whereby said first armature is actuated to, cause its switching mechanism to again. open the supervisory circuit. 7

4. In a telephone exchange system, the combination with a'telephone line extending from a substation to a central exchange, of cord connecting apparatus at the central exchange for connecting said line with another, a supervisory signal at the central exchange, anelectromagnetic device comprising two' electromagnets for jointly controlling said supervisory signal, an'armature for one of said elect-romagnets, switching mechanism absolutely controlled by saidarmature and included in the supervisory signal circuit,

an armature for the second electromagnet, switching mechanism. associated wlth said second armature, a mechanical connection normally between said armatures and servmg in cornunctlon with sald'swltchmg mechanisms to maintain the armatures in a neutral vvposition away from the poles of the w electromagnets, in which position'the' switching mechanism of the first armature is caused to open the supervisory circuit, a cir'- cuit including part of the talking circuit closed through the second electromagnet' upon connection of the cord connecting apparatus with the line, whereby said electromagnet is energized to attract its armature and to break the mechanical connection between the armatures' whereby the supervisory circuit is closed through theswitching' mechanism of the first armature, and a cir-f cuit closed through the first electromagnet upon closing ofthe. line at the substation, whereby said firstelectromagnet is energized to again open the. supervisory circuit.

'5. In a telephone exchange system, the co'n1bination "witl1 aline extending from a' substation to a central exchange, of cord connectingapp'aratus at the central exchange-- for connecting said line with'anot-her, a su-1 pervisory signal, an electromagnetic device comprising two electromagnetsfor jointly controlling said supervisory signal, an armature for one of said electromagnets, switchingniech-anism included in the supervisory circuit and absolutely controlled by said anism for said second armature tending nor.-'

. armature, said switching mechanism tending closed through the first electromagnet upon ,with said line, said jacks being provided a circuit in shunt of the switch; adapted to con:

absolutely controlled b mally to engage the first armature to prevent the switching mechanism oi the first electromagnetfrom closing the supervisory circuit, a circuit including part of the talking cir- (-uit closed through said second electromagnet upon connection of the cordconnectin apparatus with the line, whereby the secon armature is withdrawn from engagement with the first armature to allow the switching mechanism of the-first electromagnet to close the supervisory circuit, and a circuit closure of the line at a substation, whereby said first relay is energized tocause the switching-mechanism to be again open.

6. In a tele hone exchange system, the combination with a line extending from a substation to a central station, of multiple spring jacks at the central station associated with test contacts, cord connecting apparatus at the central station for connecting said line with another, an operator's telephone set, a listening key adapted to connect said telephone set wit-h the cord circuit, a switch associated with said listening key, saidswitch being adapted to open the tip strand of the cord circuit uponmanipulation of the listening key, a test circuit terminating in the tip of tlie calling plug, an electrically operated supervisory signal, and a unitary electromagnetic device having an armature tongue absolutely. controlling the circuit through said signal, and having also a second armature tongue absolutely controlled by an electric circuit closed upon the connection of said cord connecting apparatus withthe line, said first armature tongue being jointly controlled by said second armature tongue and an electric circuit closed "by a switch at the substation of a connected line and having also a switch absolutely controlled by the-second armature tongue, said switch serving during-the abnormal position of said second armature tongue to' close a trol the continuity of the tip strand of the cord circuit. 7

7 In a'- telephone exchange system, the combination with a line extending from a substation to a central station, of multiple spring jacks at the central station each provided with a test contact and associated with said line, cord-connecting apparatus at the central station forconnecting said linewith another, a listening key'and a switchadapted to open a strand of thecord circuit upon manipulation of the listening'key, a test circuit terminating ina contact of a connecting. plug, a supervisory signal, anelectromagnetic device having an armature tongue absolutely cont-rolling the operation of said su--- pervisory signal, a second armature tongue an electric circuit closed upon the connection of said-cord con-- iii necting apparatus with said line, aii electric circuit controlled. by a switch at the substation serving secondarily to control said first cuitinshunt of the'switch controlling the continuity of the cord strand.

8. In a telephone system, the combination with a telephone line extending from a sub station to a central exchange, of cord con-- for connecting said line with, another, a supervisory signal at the central exchange, an electromagnetic device comprising two elece t 'oniagnets-for controlling saidsupervisory" signal, an 'arniat-iire for one electromagnetic switching mechanism absolutely controlled by said armature and included in the supervisory circuit for said supervisory signal, said switching'mechanism having a tendency .nectingi apparatus at the central exchange" to normally close the supervisory circuit,

mechanical means associated with said armature for'normally preventing closure of the .supervisory circuit, said mechanical means being controlled by the second electromagnet vupon connection of the cord connecting apupon connection'of.the cord connecting a'pparatus with the line and closure of the line at the substation, whereby said first electromagnet becomes energized to'again open the supervisory circuit.

9. In a telephone exchange system, the

' combination with a telephone line extending its;

from a substation to anexchang e, of cord connecting apparatus 'at the exchange for connecting said line with another, asu'pervisory signal at the exchange, an electro--'i magnetic device comprising two electron agnets for jointly controlling said supervisory-t signal, an armature forone'electromagnet;

switching mechanism absolutely controlled? armature away from the electromagnet pole and to closetl e circuit through said signal, an armature for the second electromagnet,'

a spring connected with said armature tend ing to move said armature away from the pole of its electromagnet, a mechanical connection between said arinatures, whereby said spring also serves to retain the first armature and to prevent the switching I mecli 'anism controlled thereby from closing the supervisory circuit, a circuit including part of the talking circuit 'closed through said second elect-romagnet, upon connection of the cord connecting apparatus with the line whereby said electromagnet is energized to withdraw its armature from mechanical engagement with the first armature, whereby the switching inechanislncontrolled by the first armature may close the supervisory circuit, andsa circuit closed through .the first electromagnetupon closure of the line at the,

substation, whereby the armature of said first electromagnet is actuated to open the switching mechanism controlled thereby: and the supervisory circuit. 1

10. In a telephone exchange system, the combination with a telephone line extending from a substation to an exchange, of cord connecting apparatus at the exchange for connecting said line with another, a super visory signal, at the exchange, an electro-.

' magnetic device comprising two electromagnets for jointly controlling said supervisory signal, an armature for one of said electromagnets, switching mechanism controlling the supervisory circuit and controlled by said armature, a member of said switching mechanism tending normally to close the switching mechanism and'to move the ar-- mature away from the electromagnet pole, and an armaturefor the second electromagnet, said armature normally having mechanical connection with the first armature tending to maintain the first armature in position to prevent closure of the supervisory circuit at said switching mechanism, said second electromagnet being controlled upon connection of the cord connecting apparatus I change for connecting said line with another, a supervisory signal at the central exchange, an clectromagnet at the central exchange, an armature for said'electromagnet, switching mechanism included in the supervisory circuit and absolutely controlled by said armature, mechanical means for nor-7.

mally preventing actuation of the armature to close the switching mechanism and the supervlsory circuit, electromagnetic means- .-c0nt rolled upon connection of the cord con-'- nectlng apparatus with thelme for releasing said armature from said mechanical connection whereby the supervisory circuit may be closed, said electromagnet upon actuation of substation apparatus being included serially in a circuit with said electromagnetic means to actuate said armature to again open the supervisory circuit. k

12. In a telephone exchange system, the combination with a telephone line, of cord connecting apparatus at the central exchange for connecting said line with another, a supervisory signal at the central exchange, a unitary electromagnetic device for controlling said signal and comprising two electromagnets, an armature for one electro- ,magnet, switching mechanism; connected with said armature and'included in the su pervisory circuit, an arn'iaturc for the sec ond electromagnet, switching mechanism connected with said second armature, spring means associated with said switching mech anism, a mechanical connection existing normally between thearmatures and serving with said spring means to balance the armatures to normally prevent closure of the supervisorycircuit, connection of said cord connecting apparatus with the line causing current flow through the second electromagnet to destroy said balance whereby the supervisory circuit is'closed, and actuation of substation apparatus after connection of said cord connecting apparatus with the line causing the first electroniagnet to be included in a circuit with said second .electromagnet whereby said first electromagnet is energized and said supervisory circuit is again opened.

13. In a telephone exchange system, the combination with a telephone line, of a cord circuit at the central exchange for connecting said line with another, a listening key in said cord circuit, normal'contacts for said listening key normally included in the talk ing circuit, actuation of said listening key tending to disrupt the cord circuit, a supervisory signal, unitary electromagnetic mechanism comprising two electromagnets for jointly controlling said supervisory signal, an armature for one electromagnet, switching mechanism connected with said armature and controlling the supervisory circu t, an armature for said second electroinagnet, switching mechanism connected with said second armature and included in a circuit in bridge. of listening key contacts, spring means associated with said switching mechanisms, a mechanical connection existing normally between'the armatures and acting with said switching means to malntam the armatures 1n a balanced posltion to normally prevent closure of the circuits controlled by the switching mechanisms, connection of the cord connecting apparatus with the line causing current flow through the second electromagnet whereby the circuit in bridge of listening key contacts is closed whereby said listening key may be actuated thereafter without opening the cord circuit, actua o a o contacts for said llstemng key disengaged ation of said second electromagnet causing saldarmatures to-be unbalanced, whereby the supervisory circuit is also closed, and

. actuation of substation apparatus after con with the line causingcurrent nection of the cord connectin apparatus 'through the first electromagnet whereby its armature is actuated to again open the supervisory cir-' cuit.

combinationwith a telephone line extending from a substation to a central exchange, of

, cord connectingapparatus at the central ex- 9' ,sai

visory circuit, means tending normally to change for connecting said line with another, a listening key in said cord circuit,

upon actuation of said key whereby the cord circuit is opened, a supervisory signal, an electroma-gnet, an armature for said electroma et, switching mechanism controlled by armature and included in the superclose said switching mechanism and the supervisory circu1t,.mechan1cal means asso- 'ciated with said armature to normally maintain" said armature in balance to prevent closing of the switching mechanism, an additional electromagneh an armature for saidadditional electromagnet, switching met-h amsm controlled by said armature, a circuit including sald switching mechanism for bridging said listening key contacts, connection of said cord connecting apparatus with the. line causing fl'lOCfll'flI'CUll? to be closed through said second electromagnet to destroy the net and to energize the second electromagnet whereby the switching mechanism of the first electromagnet is caused to close the supervisory circuit and the switching mech- 14. In a telephone exchange system, the

' trically controlling alance of the first electromagunis-m of the second electromagnet caused to close the bridging circuit about the listening key contacts, and a circuit closed through the first electromagnet upon closure of the line at thesubstation whereby the switching mechanism of said first electromagnet is actuated to again open the supervisory circuit.

15."In a telephone exchange system, the combination with a telephone line leadin from a substation to an exchange, of a cor circuit at the exchange, a supervisory signal.

at the exchan 'e,

' visory circuit. to cause actuation of the supervisory signal, and means upon actuation of apparatus at the substation connected with. the telephone line for causing said first relay to be mcluded in a circuit with the auxiliary relay whereby the first relay is also electrically actuated to, control the supervisor'y circuitto render the supervisory signal inert.

In witness whereof, I hereunto subscribe my name this 2+lth day of February A. D., 1904.

.MERRITT S. CONNER. Witnesses:

LYNN A. WILLIAMS, JOHN STAHRQ 

